An investigation into the biosynthesis and degradation of thyrotropin releasing hormone (TRH) has demonstrated that there are two distinct enzyme systems which can play an important part in the metabolism of the tripeptide hormone. One of these is found in the hypothalamus and the other in serum. The deamidating enzyme from rat or porcine hypothalamus has been shown to be a sulfhydryl containing enzyme. Reagents which irreversibly react with sulfhydryl containing amino acids quickly and completely block TRH degradation. We have also demonstrated that the rat hypothalamus exhibits the most rapid rate of TRH degradation when compared to other areas of the brain. BIBLIOGRAPHIC REFERENCES: W.L. Taylor and J.E. Dixon (1976) Biochim. Biophys. Acta 444, 428-434 The Inhibition of Thyrotropin-Releasing Hormone Deamidation in Porcine Hypothalamic Tissue. W.L. Taylor and J.E. Dixon (1976) X International Congress of Biochemistry, 10, 548. The Inhibition of Thyrotropin Releasing Hormone Deamidation in Porcine Hypothalamic Preparations.